We have been attempting to isolate the DNA sequences which code for ribosomal RNA from human material. It is the goal of this work to determine how the sequences are organized in the nucleus of human cells and to provide purified isolated human genes which may be studied for their interaction with specific mutagens and carcinogens. It is hoped that by providing isolated pure genes of known sequence that the molecular events of carcinogen DNA interactions may be studied in fine detail. To date our preparations are only partially pure, but it is hoped that within the next six months to a year, we will have considerable quantities of isolated human rDNA sequences.